Liquid-crystalline medium and liquid-crystal display comprising 1,2-difluoroethene compounds

ABSTRACT

The present invention relates to a liquid-crystalline medium comprising 1,2-difluoroethene compounds of the general formula I, in which R 1 , ring A, Z 1 , Z 2 , m, X and L 1-6  are as defined in claim  1 . The invention also relates to the use of the medium for electro-optical purposes and to displays containing this medium. Novel 1,2-difluoroethene compounds having 3 or more rings are disclosed.

The present invention relates to a liquid-crystalline medium comprising1,2-difluoroethene compounds, and to the use thereof for electro-opticalpurposes, and to displays containing this medium. Novel1,2-difluoroethene compounds according to the invention are disclosed.

Liquid crystals are used principally as dielectrics in display devices,since the optical properties of such substances can be modified by anapplied voltage. Electro-optical devices based on liquid crystals areextremely well known to the person skilled in the art and can be basedon various effects. Examples of such devices are cells having dynamicscattering, DAP (deformation of aligned phases) cells, guest/host cells,TN cells having a twisted nematic structure, STN (supertwisted nematic)cells, SBE (super-birefringence effect) cells and OMI (optical modeinterference) cells. The commonest display devices are based on theSchadt-Helfrich effect and have a twisted nematic structure. Inaddition, there are also cells which operate with an electric fieldparallel to the substrate and liquid-crystal plane, such as the IPS(in-plane switching) cells. The TN, STN and IPS cells, in particular,are currently commercially interesting areas of application for themedia according to the invention.

The liquid-crystal materials must have good chemical and thermalstability and good stability to electric fields and electromagneticradiation. Furthermore, the liquid-crystal materials should have lowviscosity and produce short addressing times, low threshold voltages andhigh contrast in the cells.

They should furthermore have a suitable mesophase, for example a nematicor cholesteric mesophase for the above-mentioned cells, at the usualoperating temperatures, i.e. in the broadest possible range above andbelow room temperature. Since liquid crystals are generally used asmixtures of a plurality of components, it is important that thecomponents are readily miscible with one another. Further properties,such as the electrical conductivity, the dielectric anisotropy and theoptical anisotropy, have to satisfy various requirements depending onthe cell type and area of application. For example, materials for cellshaving a twisted nematic structure should have positive dielectricanisotropy and low electrical conductivity.

For example, for matrix liquid-crystal displays with integratednon-linear elements for switching individual pixels (MLC displays),media having large positive dielectric anisotropy, broad nematic phases,relatively low birefringence, very high specific resistance, good UV andtemperature stability and relatively low vapour pressure are desired.

Matrix liquid-crystal displays of this type are known. Examples ofnon-linear elements which can be used to individually switch theindividual pixels are active elements (i.e. transistors). The term“active matrix” is then used, where a distinction can be made betweentwo types:

-   1. MOS (metal oxide semiconductor) or other diodes on silicon wafers    as substrate-   2. Thin-film transistors (TFTs) on a glass plate as substrate.

The use of single-crystal silicon as substrate material restricts thedisplay size, since even modular assembly of various part-displaysresults in problems at the joints.

In the case of the more promising type 2, which is preferred, theelectro-optical effect used is usually the TN effect. A distinction ismade between two technologies: TFTs comprising compound semiconductors,such as, for example, CdSe, or TFTs based on polycrystalline oramorphous silicon. Intensive work is being carried out worldwide on thelatter technology.

The TFT matrix is applied to the inside of one glass plate of thedisplay, while the other glass plate carries the transparentcounterelectrode on its inside. Compared with the size of the pixelelectrode, the TFT is very small and has virtually no adverse effect onthe image. This technology can also be extended to fully colour-capabledisplays, in which a mosaic of red, green and blue filters is arrangedin such a way that a filter element is opposite each switchable pixel.

The TFT displays usually operate as TN cells with crossed polarisers intransmission and are backlit.

The term MLC displays here encompasses any matrix display withintegrated non-linear elements, i.e., besides the active matrix, alsodisplays with passive elements, such as varistors or diodes(MIM=metal-insulator-metal).

MLC displays of this type are particularly suitable for TV applications(for example pocket television sets) or for high-information displaysfor computer applications (laptops) and in automobile or aircraftconstruction. Besides problems regarding the angle dependence of thecontrast and the response times, difficulties also arise in MLC displaysdue to insufficiently high specific resistance of the liquid-crystalmixtures [TOGASHI, S., SEKIGUCHI, K., TANABE, H., YAMAMOTO, E.,SORIMACHI, K., TAJIMA, E., WATANABE, H., SHIMIZU, H., Proc. Eurodisplay84, September 1984: A 210-288 Matrix LCD Controlled by Double StageDiode Rings, p. 141 ff, Paris; STROMER, M., Proc. Eurodisplay 84,September 1984: Design of Thin Film Transistors for Matrix Addressing ofTelevision Liquid Crystal Displays, p. 145 ff, Paris]. With decreasingresistance, the contrast of an MLC display deteriorates, and the problemof after-image elimination may occur. Since the specific resistance ofthe liquid-crystal mixture generally drops over the life of an MLCdisplay owing to interaction with the interior surfaces of the display,a high (initial) resistance is very important in order to obtainacceptable service lives. In particular in the case of low-voltmixtures, it was hitherto impossible to achieve very high specificresistance values. It is furthermore important that the specificresistance exhibits the smallest possible increase with increasingtemperature and after heating and/or UV exposure. The low-temperatureproperties of the mixtures from the prior art are also particularlydisadvantageous. It is demanded that no crystallisation and/or smecticphases occur, even at low temperatures, and the temperature dependenceof the viscosity is as low as possible. The MLC displays from the priorart thus do not satisfy today's requirements. In addition toliquid-crystal displays which use backlighting, i.e. are operatedtransmissively and if desired transflectively, reflective liquid-crystaldisplays are also particularly interesting. These reflectiveliquid-crystal displays use the ambient light for information display.They thus consume significantly less energy than backlit liquid-crystaldisplays having a corresponding size and resolution. Since the TN effectis characterised by very good contrast, reflective displays of this typecan even be read well in bright ambient conditions. This is alreadyknown of simple reflective TN displays, as used, for example, in watchesand pocket calculators. However, the principle can also be applied tohigh-quality, higher-resolution active matrix-addressed displays, suchas, for example, TFT displays. Here, as already in the transmissiveTFT-TN displays which are generally conventional, the use of liquidcrystals of low birefringence (Δn) is necessary in order to achieve lowoptical retardation (d·Δn). This low optical retardation results inusually acceptable low viewing-angle dependence of the contrast (cf. DE30 22 818). In reflective displays, the use of liquid crystals of lowbirefringence is even more important than in transmissive displays sincethe effective layer thickness through which the light passes isapproximately twice as large in reflective displays as in transmissivedisplays having the same layer thickness.

Thus there continues to be a great demand for MLC displays having veryhigh specific resistance at the same time as a large working-temperaturerange, short response times, even at low temperatures, and a lowthreshold voltage which do not exhibit these disadvantages or only do soto a lesser extent.

In the case of TN (Schadt-Helfrich) cells, media are desired whichfacilitate the following advantages in the cells:

-   -   extended nematic phase range (in particular down to low        temperatures)    -   storage-stable, even at extremely low temperatures    -   the ability to switch at extremely low temperatures (outdoor        use, automobile, avionics)    -   increased resistance to UV radiation (longer life)

The media available from the prior art do not enable these advantages tobe achieved while simultaneously retaining the other parameters.

In the case of supertwisted (STN) cells, media are desired whichfacilitate greater multiplexability and/or a lower threshold voltageand/or broader nematic phase ranges (in particular at low temperatures).To this end, a further widening of the available parameter latitude(clearing point, smectic-nematic transition or melting point, viscosity,dielectric parameters, elastic parameters) is urgently desired.

The invention is based on the object of providing media, in particularfor MLC, TN or STN displays of this type, which do not have theabove-mentioned disadvantages or only do so to a lesser extent, andpreferably at the same time have very high specific resistance valuesand low threshold voltages.

It has now been found that this object can be achieved if mediaaccording to the invention are used in displays. The media according tothe invention are distinguished by very low rotational viscosities γ₁ incombination with a high clearing point (T_(clp.)) and goodlow-temperature properties.

JP 06329566 A and U.S. Pat. No. 5,380,461 A describe fluorinatedstilbenes which are in some cases related to the components of themixtures of the present invention. Synthetic methods for this class ofcompound are disclosed therein.

The invention relates to a liquid-crystalline medium of positivedielectric anisotropy based on a mixture of compounds, characterised inthat it comprises one or more compounds of the formula I

in which

-   R¹ denotes a halogenated or unsubstituted alkyl or alkoxy radical    having 1 to 15 C atoms, where, in addition, one or more CH₂ groups    in these radicals may each, independently of one another, be    replaced by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that    O atoms are not linked directly to one another,-   ring A denotes a ring system of the formulae

-   -   pointing to the left or right,

-   Z¹, Z² denote a single bond, —C≡C—, —CF═CF—, —CH═CH—, —CF₂O— or    —CH₂CH₂—, where at least one group from Z¹ and Z² denotes the group    —CF═CF—,

-   X denotes F, Cl, CN, SF₅ or a halogenated or unsubstituted alkyl or    alkoxy radical having 1 to 15 C atoms, where, in addition, one or    more CH₂ groups in these radicals may each, independently of one    another, be replaced by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in    such a way that O atoms are not linked directly to one another,

-   L¹, L², L³, L⁴, L⁵ and L⁶ each, independently of one another, denote    H or F, and

-   m denotes 0, 1 or 2.

Preferably, 2, 3 or 4 of the substituents L¹, L², L³ and L⁴ in theformula I denote hydrogen and the others denote F. Particular preferenceis given to media comprising compounds of the formula I in which L⁵ andL⁶=H. In the case where m=0, L¹ or L² is particularly preferably F. Inthe case where m=1 or 2, L¹ and L² are particularly preferably H. Xpreferably denotes F, Cl, OCF₃, CF₃, SF₅, OCHF₂, OC₂F₅, OC₃F₇, OCHFCF₃,OCF₂CHFCF₃ or an alkyl radical having 1 to 8 C atoms. Very particularpreference is given to compounds in which X denotes a substituent F, Cl,OCF₃ or a straight-chain alkyl radical having 1 to 6 C atoms. R¹preferably stands for an unsubstituted, straight-chain 1-6 C alkyl oralkoxy radical or a corresponding 2-6 C alkenyl radical, veryparticularly for a 1-6 C n-alkyl radical.

In order to achieve mixtures having particularly high dielectricanisotropy, the substituent X preferably denotes F, Cl, OCF₃, CF₃, SF₅,OCHF₂, OC₂F₅, OC₃F₇, OCHFCF₃ or OCF₂CHFCF₃, particularly preferably F,CF₃ or OCF₃, and very particularly preferably F or OCF₃.

The linking unit Z¹ preferably denotes a single bond or —CF═CF—. Thelinking unit Z² preferably denotes —CF═CF— or —CF₂O—. m is preferably 0or 1.

The invention furthermore relates to compounds of the formula I in whichm denotes 1 or 2, and Z² denotes a —CF═CF— bridge (compounds Ia). In thecompounds of the formula I according to the invention, the otherstructural moieties R¹, ring A, Z¹, X and L¹⁻⁶ have the meaningsindicated above and the preferred meanings indicated above.

The compounds of the formula I have a broad range of applications.Depending on the choice of substituents, these compounds can serve asbase materials of which liquid-crystalline media are predominantlycomposed; however, it is also possible to add compounds of the formula Ito liquid-crystalline base materials from other classes of compound inorder, for example, to modify the dielectric and/or optical anisotropyof a dielectric of this type and/or to optimise its threshold voltageand/or its viscosity.

In the pure state, the compounds of the formula I are colourless andform liquid-crystalline mesophases in a temperature range which isfavourably located for electro-optical use. They are stable chemicallyand thermally.

Alone and in mixtures, the compounds according to the invention have aparticularly low rotational viscosity compared with other compoundshaving comparable physical-chemical properties. In addition, theyexhibit very good overall properties, in particular with respect to theratio of the rotational viscosity to the clearing point (γ₁/clp.).

In the case where m=1 or 2 and Z¹ denotes a —CF═CF— group, the ring A ispreferably a ring system selected from the formulae

where the rings may point to both sides.

In the case where m=1 or 2 and Z² denotes a —CF═CF— group, the ring A ispreferably a ring system selected from the formulae

and

in particular from the formulae

Preferred compounds in accordance with the invention are characterisedin that, independently of one another,

-   m denotes 1,-   Z² denotes —CF═CF— and Z¹ denotes a single bond,-   X denotes F, —OCF₃, —CF₃, CN, 1-6 C n-alkyl or 1-6 C n-alkoxy, in    particular F or —OCF₃,-   L⁵ L⁶ denote H, or-   R¹ denotes 1-7 C alkyl or 2-7 C alkylene.

In the case where Z² denotes a —CF═CF— group, L³ and L⁴ are preferablyH.

Particularly preferred compounds according to the invention arecharacterised in that precisely one group from Z¹ and Z² represents a—CF═CF— group. Consequently, particularly preferred compounds accordingto the invention are those of the general formula Ib:

in which R¹, ring A, X, L¹, L², L⁵ and L⁶ are as defined above.

Particularly preferred compounds of formula I, wherein ring A is atetrahydropyran ring, are compounds of formula Ic:

If R¹ in formula I denotes an alkyl radical and/or an alkoxy radical,this may be straight-chain or branched. It is preferably straight-chain,has 2, 3, 4, 5, 6 or 7 C atoms and accordingly preferably denotes ethyl,propyl, butyl, pentyl, hexyl, heptyl, ethoxy, propoxy, butoxy, pentoxy,hexyloxy or heptyloxy, furthermore methyl, octyl, nonyl, decyl, undecyl,dodecyl, tridecyl, tetradecyl, pentadecyl, methoxy, octyloxy, nonyloxy,decyloxy, undecyloxy, dodecyloxy, tridecyloxy or tetradecyloxy.

Oxaalkyl preferably denotes straight-chain 2-oxapropyl(=methoxymethyl),2-(=ethoxymethyl) or 3-oxabutyl(=2-methoxyethyl), 2-, 3- or 4-oxapentyl,2-, 3-, 4- or 5-oxahexyl, 2-, 3-, 4-, 5- or 6-oxaheptyl, 2-, 3-, 4-, 5-,6- or 7-oxaoctyl, 2-, 3-, 4-, 5-, 6-, 7- or 8-oxanonyl, or 2-, 3-, 4-,5-, 6-, 7-, 8- or 9-oxadecyl.

If R¹ denotes an alkyl radical in which one CH₂ group has been replacedby —CH═CH—, this may be straight-chain or branched. It is preferablystraight-chain and has 2 to 10 C atoms. Accordingly, it denotes inparticular vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-,-2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4- or -5-enyl, hept-1-, -2-,-3-, -4-, -5- or -6-enyl, oct-1-, -2-, -3-, -4-, -5-, -6- or -7-enyl,non-1-, -2-, -3-, -4-, -5-, -6-, -7- or -8-enyl, or dec-1-, -2-, -3-,-4-, -5-, -6-, -7-, -8- or -9-enyl.

If R¹ denotes an alkyl radical in which one CH₂ group has been replacedby —O— and one has been replaced by —CO—, these are preferably adjacent.These thus contain an acyloxy group —CO—O— or an oxycarbonyl group—O—CO—. These are preferably straight-chain and have 2 to 6 C atoms.Accordingly, they denote in particular acetoxy, propionyloxy,butyryloxy, pentanoyloxy, hexanoyloxy, acetoxymethyl,propionyloxymethyl, butyryloxymethyl, pentanoyloxymethyl,2-acetoxyethyl, 2-propionyloxyethyl, 2-butyryloxyethyl, 3-acetoxypropyl,3-propionyloxypropyl, 4-acetoxybutyl, methoxycarbonyl, ethoxycarbonyl,propoxycarbonyl, butoxycarbonyl, pentoxycarbonyl, methoxycarbonylmethyl,ethoxycarbonylmethyl, propoxycarbonyl methyl, butoxycarbonyl methyl,2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,2-(propoxycarbonyl)ethyl, 3-(methoxycarbonyl)propyl,3-(ethoxycarbonyl)propyl or 4-(methoxycarbonyl)butyl.

If R¹ denotes an alkyl radical in which one CH₂ group has been replacedby unsubstituted or substituted —CH═CH— and an adjacent CH₂ group hasbeen replaced by CO or CO—O or O—CO, this may be straight-chain orbranched. It is preferably straight-chain and has 4 to 12 C atoms.Accordingly, it denotes in particular acryloyloxymethyl,2-acryloyloxyethyl, 3-acryloyloxypropyl, 4-acryloyloxybutyl,5-acryloyloxypentyl, 6-acryloyloxyhexyl, 7-acryloyloxyheptyl,8-acryloyloxyoctyl, 9-acryloyloxynonyl, 10-acryloyloxydecyl,methacryloyloxymethyl, 2-methacryloyloxyethyl, 3-methacryloyloxypropyl,4-methacryloyloxybutyl, 5-methacryloyloxypentyl, 6-methacryloyloxyhexyl,7-methacryloyloxyheptyl, 8-methacryloyloxyoctyl, or9-methacryloyloxynonyl.

If R¹ denotes an alkyl or alkenyl radical which is monosubstituted by CNor CF₃, this radical is preferably straight-chain. The substitution byCN or CF₃ is in any desired position.

If R¹ denotes an alkyl or alkenyl radical which is at leastmonosubstituted by halogen, this radical is preferably straight-chain,and halogen is preferably F or Cl. In the case of polysubstitution,halogen is preferably F. The resultant radicals also includeperfluorinated radicals. In the case of mono-substitution, the fluorineor chlorine substituent may be in any desired position, but ispreferably in the ω-position.

Compounds containing branched wing groups R¹ may occasionally be ofimportance owing to better solubility in the conventionalliquid-crystalline base materials, but in particular as chiral dopantsif they are optically active. Smectic compounds of this type aresuitable as components of ferroelectric materials.

Branched groups of this type generally contain not more than one chainbranch. Preferred branched radicals R¹ are isopropyl,2-butyl(=1-methylpropyl), isobutyl(=2-methylpropyl), 2-methylbutyl,isopentyl(=3-methylbutyl), 2-methylpentyl, 3-methylpentyl, 2-ethylhexyl,2-propylpentyl, isopropoxy, 2-methylpropoxy, 2-methylbutoxy,3-methylbutoxy, 2-methylpentoxy, 3-methylpentoxy, 2-ethylhexyloxy,1-methylhexyloxy, 1-methylheptyloxy.

If R¹ represents an alkyl radical in which two or more CH₂ groups havebeen replaced by —O— and/or —CO—O—, this may be straight-chain orbranched. It is preferably branched and has 3 to 12 C atoms.Accordingly, it denotes in particular biscarboxymethyl,2,2-biscarboxyethyl, 3,3-biscarboxypropyl, 4,4-biscarboxybutyl,5,5-biscarboxypentyl, 6,6-biscarboxyhexyl, 7,7-biscarboxyheptyl,8,8-biscarboxyoctyl, 9,9-biscarboxynonyl, 10,10-biscarboxydecyl,bis(methoxycarbonyl)methyl, 2,2-bis(methoxycarbonyl)ethyl,3,3-bis(methoxycarbonyl)propyl, 4,4-bis(methoxycarbonyl)butyl,5,5-bis(methoxycarbonyl)pentyl, 6,6-bis(methoxycarbonyl)hexyl,7,7-bis(methoxycarbonyl)heptyl, 8,8-bis(methoxycarbonyl)octyl,bis(ethoxycarbonyl)methyl, 2,2-bis(ethoxycarbonyl)ethyl,3,3-bis(ethoxycarbonyl)propyl, 4,4-bis(ethoxycarbonyl)butyl,5,5-bis(ethoxycarbonyl)hexyl.

The compounds of the formula I are prepared by methods known per se, asdescribed in the literature (for example in the standard works, such asHouben-Weyl, Methoden der Organischen Chemie [Methods of OrganicChemistry], Georg-Thieme-Verlag, Stuttgart), to be precise underreaction conditions which are known and suitable for the said reactions.Use can also be made here of variants known per se, which are notmentioned here in greater detail.

Suitable processes for the preparation are outlined in Scheme 1 andScheme 2.

Scheme 1 shows how the difluoroethene compounds 3 according to theinvention can be prepared by palladium-catalysed linking of achloro-difluoroethene compound of the formula 1 to a boronic acidcompound of the formula 2. The formula 3 is analogous to formula I. Theradicals Ar¹ and Ar² correspondingly represent substituted, aromaticring systems.

The starting compounds of the formula 1 can be prepared from an arylhalide 4 by halogen-metal exchange and reaction withchlorotrifluoroethylene. In the synthesis strategy shown, the desired Eisomer of the formula 3 is formed in an excess to the Z isomer. Thedesired isomer can easily be isolated by chromatography and bycrystallisation.

The invention also relates to electro-optical displays (in particularSTN or MLC displays having two plane-parallel outer plates, which,together with a frame, form a cell, integrated non-linear elements forswitching individual pixels on the outer plates, and a nematicliquid-crystal mixture of positive dielectric anisotropy and highspecific resistance located in the cell) which contain media of thistype, and to the use of these media for electro-optical purposes.

The liquid-crystal mixtures according to the invention enable asignificant broadening of the available parameter latitude. Theachievable combinations of clearing point, viscosity at low temperature,thermal stability and dielectric anisotropy are far superior to previousmaterials from the prior art.

The compounds of the formula I are, in accordance with the invention,combined with further highly polar components where Δ∈>8 and with one ormore neutral components (−1.5<Δ∈<3), at least some of whichsimultaneously have low optical anisotropy (Δn<0.08), in order to obtainthe liquid-crystalline media.

The liquid-crystal mixtures according to the invention, while retainingthe nematic phase down to −20° C. and preferably down to −30° C.,particularly preferably down to −40° C., enable a clearing point above60° C., preferably above 65° C., particularly preferably above 70° C.,simultaneously dielectric anisotropy values Δ∈ of ≧3, preferably ≧5, inparticular also ≧7, and a high value for the specific resistance to beachieved, enabling excellent STN and MLC displays to be obtained. Inparticular, the mixtures are characterised by very low rotationalviscosities. The rotational viscosities γ₁ are below 90 mPa·s,preferably below 80 mPa·s, particularly preferably below 70 mPa·s. Atthe same time, the operating voltages, depending on the selecteddielectric anisotropy of the medium, have low values.

It goes without saying that, through a suitable choice of the componentsof the mixtures according to the invention, it is also possible forhigher clearing points (for example above 90° C.) to be achieved athigher threshold voltages or lower clearing points to be achieved atlower threshold voltages with retention of the other advantageousproperties. At viscosities correspondingly increased only slightly, itis likewise possible to obtain mixtures having higher Δ∈ and thus lowthresholds or mixtures having higher clearing points. The MLC displaysaccording to the invention preferably operate at the first Gooch andTarry transmission minimum [C. H. Gooch and H. A. Tarry, Electron. Lett.10, 2-4, 1974; C. H. Gooch and H. A. Tarry, Appl. Phys., Vol. 8,1575-1584, 1975], where, besides particularly favourable electro-opticalproperties, such as, for example, high steepness of the characteristicline and low angle dependence of the contrast (DE 3022818 A1), a lowerdielectric anisotropy is sufficient at the same threshold voltage as inan analogous display at the second minimum. This enables significantlyhigher specific resistance values to be achieved using the mixturesaccording to the invention at the first minimum than in the case ofmixtures comprising cyano compounds. Through a suitable choice of theindividual components and their proportions by weight, the personskilled in the art is able to set the birefringence necessary for apre-specified layer thickness of the MLC display using simple routinemethods.

The flow viscosity ν₂₀ at 20° C. is preferably <60 mm²·s⁻¹, particularlypreferably <50 mm²·s⁻¹. The rotational viscosity γ₁ of the mixturesaccording to the invention at 20° C. is preferably <80 mPa·s,particularly preferably <70 mPa·s. The nematic phase range preferablyhas a width of at least 90° C., in particular at least 100° C. Thisrange preferably extends at least from −20° to +70° C.

A short response time is desired in liquid-crystal displays. Thisapplies in particular to displays for video reproduction. For displaysof this type, response times (total: t_(on)+t_(off)) of at most 16 msare required. The upper limit for the response time is determined by theimage refresh frequency. Besides the rotational viscosity γ₁, the tiltangle also influences the response time.

Measurements of the voltage holding ratio (HR) [S. Matsumoto et al.,Liquid Crystals 5, 1320 (1989); K. Niwa et al., Proc. SID Conference,San Francisco, June 1984, p. 304 (1984); G. Weber et al., LiquidCrystals 5, 1381 (1989)] have shown that mixtures according to theinvention comprising compounds of the formula I exhibit a significantlysmaller decrease in the HR with increasing temperature than analogousmixtures comprising cyanophenylcyclohexanes of the formula

or esters of the formula

instead of the compounds of the formula I.

Particularly preferred liquid-crystalline media comprise one or morecompounds from the formulae I-1 to I-30:

in which R¹ has the meaning indicated in formula I.

Of these preferred compounds, particularly preferred bicyclic compounds(m=0) are those of the formulae I-1, I-2, I-3, I-4 and I-5, veryparticularly those of the formulae I-1, I-2 and I-4. Of the tricycliccompounds, particular preference is given to those of the formulae I-7,I-8, I-10, I-13, I-14, I-16, I-19, I-22, I-23, I-24, I-27 and I-28, veryparticularly those of the formulae I-8 and I-14.

Preferred embodiments of the liquid-crystalline media according to theinvention are indicated below:

-   -   The liquid-crystalline medium is characterised in that the        proportion of compounds of the formula I in the mixture as a        whole is from 0.5 to 40% by weight, preferably from 4 to 20% by        weight.    -   The medium comprises one, two or more compounds of the formulae        I-1 to I-30;    -   The medium additionally comprises one or more compounds selected        from the group consisting of the general formulae II to VI:

-   -   in which the individual radicals have the following meanings:    -   R⁰ n-alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms,    -   X⁰ F, Cl, halogenated alkyl, halogenated alkenyl, halogenated        oxaalkyl, halogenated alkenyloxy or halogenated alkoxy having up        to 6 C atoms,    -   Z⁰ —C₂F₄—, —CF═CF—, —C₂H₄—, —(CH₂)₄—, —OCH₂—, —CH₂O—, —CF₂O— or        —OCF₂—,    -   Y¹ to Y⁴ each, independently of one another, H or F,    -   r 0 or 1, and    -   t 0, 1 or 2.

The compound of the formula IV is preferably

-   -   The medium additionally comprises one or more compounds selected        from the group consisting of the general formulae VII to XIII:

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms,    -   X⁰ denotes F, Cl, halogenated alkyl, halogenated alkenyl,        halogenated alkenyloxy or halogenated alkoxy having up to 6 C        atoms, and    -   Y¹ to Y⁴ each, independently of one another, denote H or F.

X⁰ here is preferably F, Cl, CF₃, OCF₃ or OCHF₂. R⁰ here preferablydenotes alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having upto 6 C atoms.

-   -   The medium additionally comprises one or more compounds of the        formulae E-a to E-d

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms.    -   The proportion of compounds of the formula I in the mixture as a        whole is from 0.5 to 40% by weight, particularly preferably from        1 to 30% by weight;    -   The proportion of the compounds of the formulae E-a to E-d is        preferably 5-30% by weight, in particular 5-25% by weight;    -   The proportion of compounds of the formulae I to VI together in        the mixture as a whole is at least 30% by weight;    -   The proportion of compounds of the formulae II to VI in the        mixture as a whole is from 30 to 80% by weight;

-   -   The medium comprises compounds of the formulae II, III, IV, V        and/or VI;    -   R⁰ in all compounds is preferably straight-chain alkyl or        alkenyl having 2 to 7 C atoms;    -   The medium comprises further compounds from the class of the        fluorinated terphenyls where R⁰ and/or X⁰, as defined below, are        end groups, preferably selected from the following group        consisting of the general formulae XIV and XV:

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms,    -   X⁰ denotes F, Cl, halogenated alkyl, halogenated alkenyl,        halogenated alkenyloxy or halogenated alkoxy having up to 6 C        atoms, and    -   rings B and C, independently of one another, denote        1,4-phenylene which is substituted by 0, 1 or 2 fluorine.

In formulae XIV and XV, at least one of the 1,4-phenylene rings ispreferably in each case mono- or polysubstituted by fluorine atoms. Incompounds of the formula XIV, preferably two of the phenylenes aresubstituted by at least one fluorine atom or one of the phenylenes issubstituted by 2 fluorine atoms; in compounds of the formula XV, one ofthe phenylenes is preferably substituted by at least one fluorine atom.X⁰ here is preferably F, Cl, CF₃, OCF₃ or OCHF₂. R⁰ here preferablydenotes alkyl, alkoxy, oxaalkyl, fluoroalkyl or alkenyl, each having upto 6 C atoms.

Compounds of the formula XIV are preferably compounds of the formulaeXIV-1 to XIV-5:

-   -   in which R⁰ is in each case, independently of one another, as        defined for the formula XIV.    -   The proportion of the compounds of the formulae XIV and XV is        preferably 0-25% by weight, in particular 2-20% by weight and        very particularly 5-15% by weight;

Compounds of the formula XV are preferably a compound of the formulaXV-1:

-   -   in which R⁰ is as defined for the formula XV.    -   The medium comprises further compounds, preferably selected from        the following group consisting of the general formulae XVI to        XVIII:

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms,    -   Y¹ denotes H or F, and    -   X⁰ denotes F, Cl, halogenated alkyl, halogenated alkenyl,        halogenated alkenyloxy or halogenated alkoxy having up to 6 C        atoms;    -   the 1,4-phenylene rings may additionally be substituted by CN,        chlorine or fluorine. The 1,4-phenylene rings are preferably        mono- or polysubstituted by fluorine atoms.    -   The medium additionally comprises one, two, three or more,        preferably two or three, compounds of the formulae

-   -   in which “alkyl” and “alkyl*” have the meaning indicated below.        The proportion of the compounds of the formulae O1 and/or O2 in        the mixtures according to the invention is preferably 0-15% by        weight, in particular 1-12% by weight and very particularly        preferably 3-10% by weight.    -   The medium preferably comprises 5-35% by weight of the compound        IVa.    -   The medium preferably comprises one, two or three compounds of        the formula IVa in which X⁰ denotes F or OCF₃.    -   The medium preferably comprises one or more compounds of the        formulae IIa to IIg

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms.

In the compounds of the formulae IIa-IIg, R⁰ preferably denotes methyl,ethyl, n-propyl, n-butyl or n-pentyl.

-   -   The medium preferably comprises one or more compounds of the        formulae K-1 to K-12 (generally K)

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms.

The proportion of compounds of the formulae K (K-1 to K-12) ispreferably from 5 to 50% by weight, particularly preferably from 10 to40% by weight.

-   -   The proportion of the compounds of the formulae IVb and/or IVc        in which X⁰ denotes fluorine and R⁰ denotes CH₃, C₂H₅, n-C₃H₇,        n-C₄H₉ or n-C₅H₁₁ in the mixture as a whole is from 2 to 20% by        weight, in particular from 2 to 15% by weight.    -   The medium preferably comprises compounds of the formulae II to        VI in which R⁰ denotes methyl. The medium according to the        invention particularly preferably comprises compounds of the        formulae

-   -   The medium preferably comprises one, two or more, preferably one        or two, dioxane compounds of the formulae

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms.

The proportion of the dioxane compounds D-1 and/or D-2 in the mixturesaccording to the invention is preferably 0-25% by weight, in particular0-20% by weight and very particularly preferably 0-15% by weight.

-   -   The medium preferably comprises one, two or more, preferably one        or two, pyran compounds of the formulae P-1 to P-4

-   -   in which    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms.    -   The medium additionally comprises one, two or more bicyclic        compounds of the formulae Z-1 to Z-9 (generally Z)

-   -   in which    -   R^(1a) and R^(2a) each, independently of one another, denote H,        CH₃, C₂H₅ or n-C₃H₇, and    -   R⁰ denotes n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each        having up to 9 C atoms.

Alkyl, alkyl* and alkenyl have the meanings indicated below.

Of the said bicyclic compounds, particular preference is given to thecompounds Z-2, Z-5, Z-4 and Z-6, very particularly the compounds of theformula Z-5 where alkyl is propyl and R^(1a) is H or methyl, inparticular where R^(1a) is H.

-   -   The proportion of compounds of the formulae Z-1 to Z-9 is in        total from 5 to 70% by weight, preferably from 15 to 50% by        weight. The proportion of compounds of the formula Z-5 alone is        preferably from 10 to 60% by weight, preferably from 15 to 50%        by weight.    -   The medium essentially consists of compounds selected from the        group consisting of the general formulae I to VI, K-1 to K-12        and from Z-1 to Z-9.

The medium additionally comprises one or more UV-stabilising compounds,in particular a quaterphenyl compound. Particular preference is given tomono- or polyfluorinated quaterphenyl compounds of the formula

where t is in each case, independently, 0, 1 or 2,

and very particularly of the formula

where n is from 1 to 8.

-   -   The medium additionally comprises one, two or more compounds        having fused rings, of the formulae AN1 to AN11:

-   -   in which R^(o) has the meanings indicated above;    -   The mixtures according to the invention are distinguished, in        particular, by the fact that they have clearing points of        ≧70° C. and threshold voltages of <2.0 V.    -   The mixtures according to the invention are distinguished, in        particular, by the fact that they have a dielectric anisotropy        of Δ∈≧3 and preferably of Δ∈>5.

It has been found that even a relatively small proportion of compoundsof the formula I mixed with conventional liquid-crystal materials, butin particular with one or more compounds of the formulae K, Z. II, III,IV, V and/or VI, results in a significant reduction in the rotationalviscosities and response times, with broad nematic phases having lowsmectic-nematic transition temperatures being observed at the same time,improving the storage stability.

The term “alkyl” or “alkyl*” encompasses straight-chain and branchedalkyl groups having 1-7 carbon atoms, in particular the straight-chaingroups methyl, ethyl, propyl, butyl, pentyl, hexyl and heptyl. Groupshaving 1-5 carbon atoms are generally preferred.

The term “alkenyl” encompasses straight-chain and branched alkenylgroups having 2-7 carbon atoms, in particular the straight-chain groups.Preferred alkenyl groups are C₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl,C₅-C₇-4-alkenyl, C₆-C₇-5-alkenyl and C₇-6-alkenyl, in particularC₂-C₇-1E-alkenyl, C₄-C₇-3E-alkenyl and C₅-C₇-4-alkenyl. Examples ofparticularly preferred alkenyl groups are vinyl, 1E-propenyl,1E-butenyl, 1E-pentenyl, 1E-hexenyl, 1E-heptenyl, 3-butenyl,3E-pentenyl, 3E-hexenyl, 3E-heptenyl, 4-pentenyl, 4Z-hexenyl,4E-hexenyl, 4Z-heptenyl, 5-hexenyl, 6-heptenyl and the like. Groupshaving up to 5 carbon atoms are generally preferred.

The term “fluoroalkyl” preferably encompasses straight-chain groupshaving a terminal fluorine, i.e. fluoromethyl, 2-fluoroethyl,3-fluoropropyl, 204-fluorobutyl, 5-fluoropentyl, 6-fluorohexyl and7-fluoroheptyl. However, other positions of the fluorine are notexcluded.

The term “oxaalkyl” or “alkoxy” preferably encompasses straight-chainradicals of the formula C_(n)H_(2n+1)—O—(CH₂)_(m), in which n and meach, independently of one another, denote 1 to 6. m may also denote 0.Preferably, n=1 and m=1-6 or m=0 and n=1-3.

Through a suitable choice of the meanings of R⁰ and X⁰, the addressingtimes, the threshold voltage, the steepness of the transmissioncharacteristic lines, etc., can be modified in the desired manner. Forexample, 1E-alkenyl radicals, 3E-alkenyl radicals, 2E-alkenyloxyradicals and the like generally result in shorter addressing times,improved nematic tendencies and a higher ratio between the elasticconstants k₃₃ (bend) and k₁₁ (splay) compared with alkyl and alkoxyradicals. 4-Alkenyl radicals, 3-alkenyl radicals and the like generallygive lower threshold voltages and lower values of k₃₃/k₁₁ compared withalkyl and alkoxy radicals.

A —CH₂CH₂— group generally results in higher values of k₃₃/k₁₁ comparedwith a single covalent bond. Higher values of k₃₃/k₁₁ facilitate, forexample, flatter transmission characteristic lines in TN cells with a90° twist (in order to achieve grey shades) and steeper transmissioncharacteristic lines in STN, SBE and OMI cells (greatermultiplexability), and vice versa.

The optimum mixing ratio of the compounds of the formulae I andK+Z+II+III+IV+V+VI depends substantially on the desired properties, onthe choice of the components of the formulae I, II, III, IV, V and/orVI, and on the choice of any further components that may be present.

Suitable mixing ratios within the range indicated above can easily bedetermined from case to case.

The total amount of compounds of the formula I and the co-componentsindicated in the mixtures according to the invention is not crucial. Themixtures can therefore comprise one or more further components for thepurposes of optimisation of various properties. However, the observedeffect on the addressing times and the threshold voltage is generallygreater, the higher the total concentration of compounds of the formulaI and the co-components indicated.

In a particularly preferred embodiment, the media according to theinvention comprise compounds of the formulae II to VI (preferably II,III and/or IV, in particular IVa) in which X⁰ denotes F, OCF₃, OCHF₂,OCH═CF₂, OCF═CF₂ or OCF₂—CF₂H. A favourable synergistic effect with thecompounds of the formula I results in particularly advantageousproperties. In particular, mixtures comprising compounds of the formulaI and formula IVa are distinguished by their low threshold voltage.

The individual compounds which can be used in the media according to theinvention are either known or can be prepared analogously to the knowncompounds.

The construction of the MLC display according to the invention frompolarisers, electrode base plates and surface-treated electrodescorresponds to the usual design for displays of this type. The termusual design is broadly drawn here and also encompasses all derivativesand modifications of the MLC display, in particular including matrixdisplay elements based on poly-Si TFTs or MIM.

A significant difference between the displays according to the inventionand the hitherto conventional displays based on the twisted nematic cellconsists, however, in the choice of the liquid-crystal parameters of theliquid-crystal layer.

The liquid-crystal mixtures which can be used in accordance with theinvention are prepared in a manner conventional per se. In general, thedesired amount of the components used in lesser amount is dissolved inthe components making up the principal constituent, advantageously atelevated temperature. It is also possible to mix solutions of thecomponents in an organic solvent, for example in acetone, chloroform ormethanol, and to remove the solvent again, for example by distillation,after thorough mixing.

The dielectrics may also comprise further additives known to the personskilled in the art and described in the literature, such as, forexample, UV stabilisers, such as Tinuvin® from Ciba, antioxidants,free-radical scavengers, etc. For example, 0-15% of pleochroic dyes orchiral dopants can be added. Suitable stabilisers and dopants arementioned below in Tables C and D.

The threshold voltage V₁₀ denotes the voltage for 10% transmission(viewing angle perpendicular to the plate surface). t_(on) denotes theswitch-on time and t_(off) the switch-off time at an operating voltagecorresponding to 2.0 times the value of V₁₀. Δn denotes the opticalanisotropy. Δ∈ denotes the dielectric anisotropy (Δ∈=∈_(∥)−∈_(⊥), where∈_(∥) denotes the dielectric constant parallel to the longitudinalmolecular axes and ∈_(⊥) denotes the dielectric constant perpendicularthereto). The electro-optical data are measured in a TN cell at the 1stminimum (i.e. at a d·Δn value of 0.5 μm) at 20° C., unless expresslystated otherwise. The optical data are measured at 20° C., unlessexpressly stated otherwise.

In the present application and in the examples below, the structures ofthe liquid-crystal compounds are indicated by means of acronyms, thetrans-formation into chemical formulae taking place in accordance withTables A and B below. All radicals C_(n)H_(2n+1) and C_(m)H_(2m+1) arestraight-chain alkyl radicals having n and m C atoms respectively; n andm are integers and preferably denote 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,11 or 12. The coding in Table B is self-evident. In Table A, only theacronym for the parent structure is indicated. In individual cases, theacronym for the parent structure is followed, separated by a dash, by acode for the substituents R^(1*), R^(2*), L^(1*) and L^(2*):

Code for R¹*, R²*, L¹*, L²*, L³* R¹* R²* L¹* L²* nm C_(n)H_(2n+1)C_(m)H_(2m+1) H H n0m OC_(n)H_(2n+1) C_(m)H_(2m+1) H H n0•mC_(n)H_(2n+1) OC_(m)H_(2m+1) H H n C_(n)H_(2n+1) CN H H nN•FC_(n)H_(2n+1) CN F H nN•F•F C_(n)H_(2n+1) CN F F nF C_(n)H_(2n+1) F H HnCl C_(n)H_(2n+1) Cl H H n0F OC_(n)H_(2n+1) F H H nF•F C_(n)H_(2n+1) F FH nF•F•F C_(n)H_(2n+1) F F F nmF C_(n)H_(2n+1) C_(m)H_(2m+1) F H n0CF₃C_(n)H_(2n+1) OCF₃ H H n0CF₃•F C_(n)H_(2n+1) OCF₃ F H n0CF₃•F•FC_(n)H_(2n+1) OCF₃ F F n-Vm C_(n)H_(2n+1) —CH═CH—C_(m)H_(2m+1) H H nV-VmC_(n)H_(2n+1)—CH═CH— —CH═CH—C_(m)H_(2m+1) H H

Preferred mixture components are found in Tables A and B.

TABLE A

TABLE B

Particular preference is given to liquid-crystalline mixtures which,besides the compounds of the formula I, comprise at least one, two,three or four compounds from Table B.

TABLE C Table C indicates possible dopants which are generally added tothe mixtures according to the invention. The mixtures preferablycomprise 0-10% by weight, in particular 0.01-5% by weight andparticularly preferably 0.01-3% by weight of dopants.

TABLE D Stabilisers which can be added, for example, to the mixturesaccording to the invention are mentioned below.

The following examples explain the invention without intending torestrict it. The person skilled in the art will be able to takeparticularly suitable embodiments, which are not described in greaterdetail, from the examples and adapt them to different boundaryconditions.

Above and below, percentages denote percent by weight. All temperaturesare indicated in degrees Celsius. C=crystalline state, N=nematic phase,Sm=smectic phase and I=isotropic phase. The data between these symbolsrepresent the transition temperatures for the pure substances.

The physical measurement methods on mixtures are described in “MerckLiquid Crystals, Physical Properties of Liquid Crystals”, November 1997,Merck KGaA.

The dielectric anisotropy Δ∈ of the individual substances is determinedat 20° C. and 1 kHz. To this end, 10% by weight of the substances to beinvestigated are measured dissolved in the dielectrically positivemixture ZLI-4792 (Merck KGaA), and the measurement value is extrapolatedto a concentration of 100%. The optical anisotropy Δn is determined at20° C. and a wavelength of 589.3 nm. It is likewise determined byextrapolation of the values at 10% by weight.

The following abbreviations are used:

-   clp. clearing point (nematic-isotropic phase transition    temperature),-   Δn optical anisotropy (589 nm, 20° C.), Δ∈ dielectric anisotropy (1    kHz, 20° C.), ∈_(∥)−∈_(⊥)-   ∈_(∥) proportion of the dielectric constant parallel to the    longitudinal molecular axis (1 kHz, 20° C.),-   ∈_(⊥) proportion of the dielectric constant perpendicular to the    longitudinal molecular axis (1 kHz, 20° C.),-   γ₁ rotational viscosity (20° C.),-   t_(store) low-temperature storage stability in hours (−20° C., −30°    C., −40° C.),-   V₁₀ threshold voltage=characteristic voltage at a relative contrast    of 10%,-   V₉₀ saturation voltage=characteristic voltage at a relative contrast    of 90%,-   k₁ elastic constant (splay deformation, also k₁₁),-   k₃ elastic constant (bend deformation, also k₃₃),-   k₃/k₁ ratio of k₃ to k₁,-   V₀ capacitive or Freederickzs threshold voltage.

SYNTHESIS EXAMPLE 1.1

A Grignard solution is prepared by slow addition of 141 g (70.9 mmol) of1-bromo-4-propylbenzene to 20 g (823 mmol) of magnesium in 200 ml of dryTHF. After stirring under reflux for 1 h, the mixture is diluted with 1l of THF and cooled to −35° C. 100 g (0.86 mol) ofchlorotrifluoroethylene are slowly passed in on a dry-ice condenser, andthe mixture is stirred for 1.5 h. The reaction solution is warmed to RT,stirred for 12 h and stirred into an ice/2 N HCl mixture. The organicphase is separated off. The aqueous phase is extracted with MTB ether.The combined organic phases are washed with water and NaCl solution,dried and evaporated. The product is a colourless liquid.

SYNTHESIS EXAMPLE 1.2

2.02 g (30 mmol) of bis(tricyclohexylphosphine)palladium(II) chlorideand 0.154 ml (30 mmol) of hydrazinium hydroxide are added to 18.2 g (97mmol) of sodium orthosilicate in 50 ml of water under nitrogen, and themixture is stirred for 5 min. 32.5 g (142 mmol) of the product fromExample 1.1 and 50 g (141 mmol) of the boronic acid compound are added,and the mixture is stirred under reflux for 12 h. The organic phase issubsequently separated off, the remainder is washed by shaking, and allorganic phases are combined. The purification is carried out byfractionation over 1 l of silica gel using pentane. The product fractionis crystallised from cold isopropanol. Colourless crystals (m.p. 55°C., >99% GC/HPLC). C 55 N 75 I.

SYNTHESIS EXAMPLE 2

0.40 g (0.72 mmol) of bis(tricyclohexylphosphine)palladium(II) chlorideand 0.35 ml (0.72 mmol) of hydrazinium chloride are added to 3.75 g(19.9 mmol) of sodium orthosilicate in 10 ml of water under nitrogen,and the mixture is stirred for 5 min. 7.23 g (28 mmol) of the boronicacid and 7.50 g (27 mmol) of the chlorodifluoroethene compound areadded, and the mixture is stirred under reflux for 12 h. After work-upanalogously to Example 1.1, the product is crystallised fromtoluene/methanol (m.p. 39° C., >99% GC/HPLC). C 39 SmB 110 SmA 221 N 226I.

clp. 215.5° C. Δε 8.4 Δn 0.223 γ₁ 249 mPa · s

MIXTURE EXAMPLE 1

CC-3-V  26% Clearing point [° C.]: 73.5 CC-3-V1  7% Δn [589 nm, 20° C.]:0.1007 CCQU-3-F  12% Δε [1 kHz, 20° C.]: +7.8 PUQU-2-F  9% γ₁ [mPa · s,20° C.]: 57 PUQU-3-F  12% V₁₀ [V]: 1.48 CCP-V-1  14% CCP-30CF3  8%CCGU-3-F  3% CBC-33  1%

 8% 100%

MIXTURE EXAMPLE 2

CCP-30CF3  4% Clearing point [° C.]: 78.0 CCQU-3-F  12% Δn [589 nm, 20°C.]: 0.102 CC-4-V  14% Δε [1 kHz, 20° C.]: +9.7 CC-3-V1  14% γ₁ [mPa ·s, 20° C.]: 72 PUQU-2-F  14% V₁₀ [V]: 1.34 PUQU-3-F  13% CCP-V-1  20%CCGU-3-F  5%

 4% 100%

MIXTURE EXAMPLE 3

CC-3-V1  17% Clearing point [° C.]: 76.0 CC-3-V  31% Δn [589 nm, 20°C.]: 0.102 PUQU-2-F  9% Δε [1 kHz, 20° C.]: +5.5 PUQU-3-F  8% γ₁ [mPa ·s, 20° C.]: 52 BCH-32  4% V₁₀ [V]: 1.86 CCP-V-1  14% CCGU-3-F  9%

 8% 100%

MIXTURE EXAMPLE 4

CC-3-V1  17% Clearing point [° C.]: 76 CC-3-V  31% Δn [589 nm, 20° C.]:0.1023 PUQU-2-F  9% Δε [1 kHz, 20° C.]: +5.5 PUQU-3-F  8% γ₁ [mPa · s,20° C.]: 52 BCH-32  4% V₁₀ [V]: 1.86 CCP-V-1  14% CCGU-3-F  9%

 8% 100%

MIXTURE EXAMPLE 5

CC-3-V1  15% Clearing point [° C.]: 75.5 CC-3-V  31% Δn [589 nm, 20°C.]: 0.1066 PUQU-2-F  8% Δε [1 kHz, 20° C.]: +5.3 PUQU-3-F  8% γ₁ [mPa ·s, 20° C.]: 49 BCH-32  8% V₁₀ [V]: 1.90 CCP-V-1  11% CCGU-3-F  8%PP-1-2V1  3%

 8% 100%

MIXTURE EXAMPLE 6

PUQU-2-F  7% Clearing point [° C.]: 77.5 PUQU-3-F  10% Δn [589 nm, 20°C.]: 0.1158 CC-3-V  36% Δε [1 kHz, 20° C.]: +7.1 CCP-V-1  15% γ₁ [mPa ·s, 20° C.]: 57 CCGU-3-F  8% V₁₀ [V]: 1.60 BCH-32  10% PGU-3-F  6%

 8% 100%

MIXTURE EXAMPLE 7

CC-3-V1  18% Clearing point [° C.]: 75 CC-3-V  31% Δn [589 nm, 20° C.]:0.1082 PUQU-2-F  8% Δε [1 kHz, 20° C.]: +5.5 PUQU-3-F  11% γ₁ [mPa · s,20° C.]: 50 BCH-32  10% V₁₀ [V]: 1.82 CCP-V-1  6% CCGU-3-F  8%

 8% 100%

MIXTURE EXAMPLE 8

PUQU-3-F  18% Clearing point [° C.]: 75.5 CC-3-V  31% Δn [589 nm, 20°C.]: 0.1090 CC-3-V1  10% Δε [1 kHz, 20° C.]: +7.0 CCP-V-1  8% γ₁ [mPa ·s, 20° C.]: 57 CCGU-3-F  8% V₁₀ [V]: 1.65 BCH-32  10% PGU-3-F  7%

 8% 100%

MIXTURE EXAMPLE 9

PUQU-3-F  16% Clearing point [° C.]: 75.5 CC-3-V  43% Δn [589 nm, 20°C.]: 0.1226 CCGU-3-F  7% Δε [1 kHz, 20° C.]: +7.1 BCH-32  6% γ₁ [mPa ·s, 20° C.]: 56 APUQU-3-F  6% V₁₀ [V]: 1.66 PGP-2-4  7% PGP-2-3  4%CBC-33  3%

 8% 100%

MIXTURE EXAMPLE 10

PUQU-3-F   16% Clearing point [° C.]: 74.5 CC-3-V 43.5% Δn [589 nm, 20°C.]: 0.1201 CCGU-3-F   9% Δε [1 kHz, 20° C.]: +7.1 BCH-32  5.5% γ₁ [mPa· s, 20° C.]: 57 APUQU-3-F   6% V₁₀ [V]: 1.64 PGP-2-4   5% PGP-2-3   4%CBC-33   3%

  8%  100%

MIXTURE EXAMPLE 11

PUQU-3-F  10% Clearing point [° C.]: 75 CC-3-V  43% Δn [589 nm, 20° C.]:0.1084 CC-3-V1  13% Δε [1 kHz, 20° C.]: +5.3 CCGU-3-F  7% γ₁ [mPa · s,20° C.]: 48 APUQU-3-F  6% V₁₀ [V]: 1.88 PGP-2-4  6% PGP-2-3  4% CBC-33 3%

 8% 100%

MIXTURE EXAMPLE 12

CC-3-V  40% Clearing point [° C.]: 74.5 CC-3-V1  11% Δn [589 nm, 20°C.]: 0.1187 PUQU-3-F  3% Δε [1 kHz, 20° C.]: +4.6 PGU-2-F  7% γ₁ [mPa ·s, 20° C.]: 49 PGU-3-F  10% V₁₀ [V]: 1.94 PGP-2-3  5% PGP-2-4  3.5%CCP-30CF3  2% CCP-V-1  6.5% CCGU-3-F  3% CBC-33  3%

 6% 100%

MIXTURE EXAMPLE 13

PUQU-3-F  17% Clearing point [° C.]: 76 CC-3-V  37% Δn [589 nm, 20° C.]:0.1193 CC-3-V1  5% Δε [1 kHz, 20° C.]: +7.3 CCP-V-1  6% γ₁ [mPa · s, 20°C.]: 56 CCGU-3-F  8% V₁₀ [V]: 1.64 BCH-32  10% PGU-3-F  5% PPGU-4-F  3%PGP-2-3  3%

 6% 100%

MIXTURE EXAMPLE 14

CC-3-V1  15% Clearing point [° C.]: 76 CC-3-V  36% Δn [589 nm, 20° C.]:0.1092 PUQU-3-F  16% Δε [1 kHz, 20° C.]: +5.6 BCH-32  10% γ₁ [mPa · s,20° C.]: 51 CCP-V-1  4% V₁₀ [V]: 1.87 CCGU-3-F  7% PPGU-4-F  3% PGP-2-4 3%

 6% 100%

MIXTURE EXAMPLE 15

PUQU-3-F  17% Clearing point [° C.]: 75 CC-3-V  38% Δn [589 nm, 20° C.]:0.1184 CCP-V-1  9% Δε [1 kHz, 20° C.]: +7.0 CCGU-3-F  10% γ₁ [mPa · s,20° C.]: 58 BCH-32  10% V₁₀ [V]: 1.65 PGU-3-F  6% PGP-2-4  4%

 6% 100%

MIXTURE EXAMPLE 16

PGU-2-F  5% Clearing point [° C.]: 75.0 CDU-2-F  6% Δn [589 nm, 20° C.]:0.0972 CCZU-3-F  15% Δε [1 kHz, 20° C.]: +8.5 CC-3-V1  13% γ₁ [mPa · s,20° C.]: 61 CC-3-V  21% k₁ [pN, 20° C.] 13.1 CCP-V-1  6% k₃/k₁ [pN, 20°C.] 0.95 CCP-30CF3  8% V₀ [V, 20° C.] 1.30 CCP-40CF3  6% PUQU-2-F  7%PUQU-3-F  7%

 6% 100%

MIXTURE EXAMPLE 17

PGU-2-F  6.5% Clearing point [° C.]: 75.5 CDU-2-F  4.5% Δn [589 nm, 20°C.]: 0.0976 CCZU-3-F  12% Δε [1 kHz, 20° C.]: +8.4 CC-3-V1  13% γ₁ [mPa· s, 20° C.]: 61 CC-3-V  21% k₁ [pN, 20° C.] 12.6 CCP-V-1  8% k₃/k₁ [pN,20° C.] 1.02 CCP-30CF3  8% V₀ [V, 20° C.] 1.29 CCP-40CF3  8% PUQU-2-F 7% PUQU-3-F  6%

 6% 100%

MIXTURE EXAMPLE 18

CC-3-V  19% Clearing point [° C.]: 75.5 CC-3-V1  13% Δn [589 nm, 20°C.]: 0.0975 CCP-30CF3  8% Δε [1 kHz, 20° C.]: +8.6 CCP-40CF3  8% γ₁ [mPa· s, 20° C.]: 65 CCP-V-1  8% k₁ [pN, 20° C.] 12.5 CCZU-3-F  13% k₃/k₁[pN, 20° C.] 1.01 CDU-2-F  6.5% V₀ [V, 20° C.] 1.27 PGU-2-F  5.5%PUQU-2-F  7% PUQU-3-F  6%

 6% 100%

MIXTURE EXAMPLE 19

CC-3-V   13% Clearing point [° C.]: 78.5 CC-3-V1   12% Δn [589 nm, 20°C.]: 0.1105 CCGU-3-F   5% Δε [1 kHz, 20° C.]: +11.4 CCP-30CF3   8% γ₁[mPa · s, 20° C.]: 78 CCP-V-1 10.5% k₁ [pN, 20° C.] 13.0 CCZU-3-F   12%k₃/k₁ [pN, 20° C.] 0.98 CDU-2-F   9% V₀ [V, 20° C.] 1.12 PGU-2-F  7.5%PUQU-2-F  8.5% PUQU-3-F  8.5%

  6%  100%

MIXTURE EXAMPLE 20

CC-3-V 14.5% Clearing point [° C.]: 79.0 CC-3-V1   12% Δn [589 nm, 20°C.]: 0.1097 CCGU-3-F   7% Δε [1 kHz, 20° C.]: +11.3 CCP-30CF3   7% γ₁[mPa · s, 20° C.]: 78 CCP-V-1 12.5% k₁ [pN, 20° C.] 12.4 CCZU-3-F   9%k₃/k₁ [pN, 20° C.] 1.06 CDU-2-F   7% V₀ [V, 20° C.] 1.10 PGU-2-F   8%PUQU-2-F  8.5% PUQU-3-F  8.5%

  6%  100%

MIXTURE EXAMPLE 21

CC-3-V 12.5% Clearing point [° C.]: 79 CC-3-V1   12% Δn [589 nm, 20°C.]: 0.1100 CCGU-3-F   7% Δε [1 kHz, 20° C.]: +11.4 CCP-30CF3   8% γ₁[mPa · s, 20° C.]: 81 CCP-V-1 12.5% k₁ [pN, 20° C.] 12.2 CCZU-3-F   9%k₃/k₁ [pN, 20° C.] 1.07 CDU-2-F   9% V₀ [V, 20° C.] 1.09 PGU-2-F   7%PUQU-2-F  8.5% PUQU-3-F  8.5%

  6%  100%

MIXTURE EXAMPLE 22

APUQU-2-F   8% Clearing point [° C.]: 73.0 CC-3-V   25% Δn [589 nm, 20°C.]: 0.1005 CC-3-V1   13% Δε [1 kHz, 20° C.]: +8.6 CCP-V-1 10.5% γ₁ [mPa· s, 20° C.]: 59 CCP-V2-1   10% k₁ [pN, 20° C.] 12.8 CDU-2-F   10% k₃/k₁[pN, 20° C.] 1.01 PUQU-2-F  8.5% V₀ [V, 20° C.] 1.28 PUQU-3-F   9%

  6%  100%

MIXTURE EXAMPLE 23

APUQU-2-F   8% Clearing point [° C.]: 74.5 CC-3-V   26% Δn [589 nm, 20°C.]: 0.0996 CC-3-V1   12% Δε [1 kHz, 20° C.]: +8.5 CCP-V-1 10.5% γ₁ [mPa· s, 20° C.]: 59 CCP-V2-1   12% k₁ [pN, 20° C.] 12.7 CDU-2-F   8% k₃/k₁[pN, 20° C.] 1.05 PGU-2-F   2% V₀ [V, 20° C.] 1.28 PUQU-2-F  7.5%PUQU-3-F   8%

  6%  100%

MIXTURE EXAMPLE 24

APUQU-2-F   8% Clearing point [° C.]: 73 CC-3-V   25% Δn [589 nm, 20°C.]: 0.1000 CC-3-V1   12% Δε [1 kHz, 20° C.]: +8.5 CCP-V-1 10.5% γ₁ [mPa· s, 20° C.]: 60 CCP-V2-1   12% k₁ [pN, 20° C.] 12.2 CDU-2-F  9.5% k₃/k₁[pN, 20° C.] 1.07 PGU-2-F  1.5% V₀ [V, 20° C.] 1.25 PUQU-2-F  7.5%PUQU-3-F   8%

  6%  100%

MIXTURE EXAMPLE 25

APUQU-2-F  9% Clearing point [° C.]: 78 CC-3-V  16% Δn [589 nm, 20° C.]:0.1118 CC-3-V1  12% Δε [1 kHz, 20° C.]: +11.1 CCP-30CF3  7% γ₁ [mPa · s,20° C.]: 74 CCP-V-1  11% CCP-V2-1  10% CDU-2-F  5.5% PGU-2-F  5%PUQU-2-F  10% PUQU-3-F  10%

 4.5% 100%

MIXTURE EXAMPLE 26

APUQU-2-F   9% Clearing point [° C.]: 79.5 CC-3-V 15.5% Δn [589 nm, 20°C.]: 0.1112 CC-3-V1   12% Δε [1 kHz, 20° C.]: +11.1 CCP-30CF3  7.5% γ₁[mPa · s, 20° C.]: 72 CCP-V-1 11.5% CCP-V2-1   11% CDU-2-F  3.5% PGU-2-F  5% PUQU-2-F   10% PUQU-3-F   10%

  5%  100%

MIXTURE EXAMPLE 27

APUQU-2-F   9% Clearing point [° C.]: 78.5 CC-3-V 14.5% Δn [589 nm, 20°C.]: 0.1114 CC-3-V1   12% Δε [1 kHz, 20° C.]: +11.2 CCP-30CF3  7.5% γ₁[mPa · s, 20° C.]: 76 CCP-V-1 11.5% k₁ [pN, 20° C.] 12.7 CCP-V2-1   11%k₃/k₁ [pN, 20° C.] 1.08 CDU-2-F   5% V₀ [V, 20° C.] 1.12 PGU-2-F  4.5%PUQU-2-F   10% PUQU-3-F   10%

  5%  100%

MIXTURE EXAMPLE 28

CC-3-V  21% Clearing point [° C.]: 74 CC-3-V1  6% Δn [589 nm, 20° C.]:0.1192 CCQU-2-F  11% Δε [1 kHz, 20° C.]: +11.2 PUQU-3-F  17% ε_(∥) [1kHz, 20° C.]: +15.0 PGU-2-F  7% γ₁ [mPa · s, 20° C.]: 77 PGU-3-F  12%V₁₀ [V]: 1.23 CCP-V-1  17% V₉₀ [V]: 1.88 CCGU-3-F  3%

 6% 100%

MIXTURE EXAMPLE 29

CC-3-V  42% Clearing point [° C.]: 75 CC-3-V1  12% Δn [589 nm, 20° C.]:0.1210 PP-1-2V1  1% Δε [1 kHz, 20° C.]: +4.3 PGU-2-F  8% ε_(∥) [1 kHz,20° C.]: +7.2 PGU-3-F  12% γ₁ [mPa · s, 20° C.]: 49 PGP-2-3  6% V₁₀ [V]:2.10 PGP-2-4  5% V₉₀ [V]: 3.08 CCP-V-1  6%

 8% 100%

MIXTURE EXAMPLE 30

CC-3-V  41% Clearing point [° C.]: 74.5 CC-3-V1  6% Δn [589 nm, 20° C.]:0.1204 PP-1-2V1  3% Δε [1 kHz, 20° C.]: +4.0 PGU-2-F  6% ε_(∥) [1 kHz,20° C.]: +7.1 PGU-3-F  8% γ₁ [mPa · s, 20° C.]: — PGP-2-3  6% V₁₀ [V]: —PGP-2-4  6% V₉₀ [V]: — CCP-V-1  17%

 7% 100%

MIXTURE EXAMPLE 31

CC-3-V  24% Clearing point [° C.]: 75.5 CCQU-2-F  6% Δn [589 nm, 20°C.]: 0.1210 PUQU-3-F  17% Δε [1 kHz, 20° C.]: +12.7 PGU-2-F  5% ε_(∥) [1kHz, 20° C.]: +16.4 PGU-3-F  6% γ₁ [mPa · s, 20° C.]: 82 CCP-30CF3  8%V₁₀ [V]: 1.21 PGP-2-3  1% V₉₀ [V]: 1.88 CCP-V-1  18% CCGU-3-F  3%

 12% 100%

MIXTURE EXAMPLE 32

CC-3-V  24% Clearing point [° C.]: 77.5 CCQU-2-F  6% Δn [589 nm, 20°C.]: 0.1209 PUQU-3-F  17% Δε [1 kHz, 20° C.]: +12.2 PGU-2-F  5% ε_(∥) [1kHz, 20° C.]: +15.9 PGU-3-F  6% γ₁ [mPa · s, 20° C.]: 78 CCP-30CF3  8%V₁₀ [V]: 1.25 PGP-2-3  2% V₉₀ [V]: 1.90 CCP-V-1  18% CCGU-3-F  4%

 10% 100%

MIXTURE EXAMPLE 33

PGU-2-F   4% Clearing point [° C.]: 69 PUQU-2-F   8% Δn [589 nm, 20°C.]: 0.1091 GGP-3-CL   4% Δε [1 kHz, 20° C.]: +4.1 CC-3-V 35.5% ε_(∥) [1kHz, 20° C.]: +6.9 CC-3-V1   13% γ₁ [mPa · s, 20° C.]: 47 PP-1-2V1   9%k₁ [pN, 20° C.] 13.0 CCP-V-1   11% k₃/k₁ [pN, 20° C.] 1.06 CCP-V2-1 2.5% V₀ [V, 20° C.] 1.88 BCH-32   8%

  5%  100%

MIXTURE EXAMPLE 34

CDU-2-F   2% Clearing point [° C.]: 75.5 PGU-2-F   3% Δn [589 nm, 20°C.]: 0.0996 PUQU-2-F  7.5% Δε [1 kHz, 20° C.]: +8.7 PUQU-3-F   8% ε_(∥)[1 kHz, 20° C.]: +12.1 CCP-V-1   11% γ₁ [mPa · s, 20° C.]: 59 CCP-V2-111.5% k₁ [pN, 20° C.] 12.4 CC-3-V1 12.5% k₃/k₁ [pN, 20° C.] 1.12 CC-3-V30.5% V₀ [V, 20° C.] 1.25 APUQU-2-F   8%

  6%  100%

MIXTURE EXAMPLE 35

CDU-2-F  4.5% Clearing point [° C.]: 74 PGU-2-F   5% Δn [589 nm, 20°C.]: 0.1000 PUQU-2-F   8% Δε [1 kHz, 20° C.]: +8.6 PUQU-3-F   8% ε_(∥)[1 kHz, 20° C.]: +12.1 CCP-V-1   11% γ₁ [mPa · s, 20° C.]: 60 CCP-V2-1  6% k₁ [pN, 20° C.] 12.1 CC-3-V1   12% k₃/k₁ [pN, 20° C.] 1.10 CC-3-V31.5% V₀ [V, 20° C.] 1.25 APUQU-2-F   8%

  6%  100%

MIXTURE EXAMPLE 36

CCP-30CF3   7% Clearing point [° C.]: 80 PGU-2-F  5.5% Δn [589 nm, 20°C.]: 0.1096 PUQU-2-F  8.5% Δε [1 kHz, 20° C.]: +10.9 PUQU-3-F   9% ε_(∥)[1 kHz, 20° C.]: +14.4 CC-3-V1   12% γ₁ [mPa · s, 20° C.]: 71 CC-3-V21.5% k₁ [pN, 20° C.] 13.0 CCP-V-1 11.5% k₃/k₁ [pN, 20° C.] 1.08CCP-V2-1   10% V₀ [V, 20° C.] 1.15 APUQU-2-F  8.5%

 6.5%  100%

MIXTURE EXAMPLE 37

PUQU-2-F  11% Clearing point [° C.]: 75 PUQU-3-F  9.5% Δn [589 nm, 20°C.]: 0.1001 CCP-30CF3  8% Δε [1 kHz, 20° C.]: +13.9 CC-3-V  25% ε_(∥) [1kHz, 20° C.]: +17.9 CC-3-V1  11% γ₁ [mPa · s, 20° C.]: 79 CCZU-3-F  1.5%k₁ [pN, 20° C.] 11.4 CCQU-3-F  10% k₃/k₁ [pN, 20° C.] 1.11 CCGU-3-F  10%V₀ [V, 20° C.] 0.96 APUQU-2-F  9%

 5% 100%

MIXTURE EXAMPLE 38

PUQU-2-F  11% Clearing point [° C.]: 75.5 PUQU-3-F  9.5% Δn [589 nm, 20°C.]: 0.0996 CCZU-3-F  9.5% Δε [1 kHz, 20° C.]: +13.4 CC-3-V  35% ε_(∥)[1 kHz, 20° C.]: +17.5 CCQU-3-F  10% γ₁ [mPa · s, 20° C.]: 80 CCGU-3-F 9% k₁ [pN, 20° C.] 11.0 APUQU-2-F  9% k₃/k₁ [pN, 20° C.] 1.07 V₀ [V,20° C.] 0.95

 7% 100%

1. A liquid-crystalline medium of positive dielectric anisotropy basedon a mixture of compounds, said medium comprising one or more compoundsof the formula I

in which R¹ is a halogenated or unsubstituted alkyl or alkoxy radicalhaving 1 to 15 C atoms, where, in addition, one or more CH₂ groups inthese radicals are each, independently of one another, optionallyreplaced by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that Oatoms are not linked directly to one another, ring A is a ring system ofthe formulae

 pointing to the left or right, Z¹, Z² are each, independently, a singlebond, —C≡C—, —CF═CF—, —CH═CH—, —CF₂O— or —CH₂CH₂—, where at least one ofZ¹ and Z² is —CF═CF—, X is F, Cl, CN, SF₅ or a halogenated orunsubstituted alkyl or alkoxy radical having 1 to 15 C atoms, where, inaddition, one or more CH₂ groups in these radicals are each,independently of one another, optionally replaced by —C≡C—, —CH═CH—,—O—, —CO—O— or —O—CO— in such a way that O atoms are not linked directlyto one another, L¹, L², L³, L⁴, L⁵ and L⁶ are each, independently of oneanother, H or F, and m is 0 or 1; and said medium further comprises oneor more compounds of formulae K-1 to K-12:

in which R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having upto 9 C atoms.
 2. A liquid-crystalline medium according to claim 1,wherein said medium comprises one, two or more compounds of the formulaeI-1 to I-30:

in which R¹ is a halogenated or unsubstituted alkyl or alkoxy radicalhaving 1 to 15 C atoms, where, in addition, one or more CH₂ groups inthese radicals are each, independently of one another, optionallyreplaced by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that Oatoms are not linked directly to one another, and n stands for 1, 2, 3,4, 5, 6, 7 or
 8. 3. A liquid-crystalline medium according to claim 1,wherein said medium further comprises one or more compounds of formulaeZ-1 to Z-9:

in which R^(1a) and R^(2a) are each, independently of one another, H,CH₃, C₂H₅ or n-C₃H₇, R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl,each having up to 9 C atoms, alkyl, alkyl* are each, independently, anunsubstituted n-alkyl radical having 1 to 7 C atoms, and alkenyl is anunsubstituted alkenyl radical having 2-7 C atoms.
 4. Aliquid-crystalline medium according to claim 1, wherein said mediumfurther comprises one or more compounds selected from formulae II, III,IV, V and VI

in which R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having upto 9 C atoms, X⁰ is F, Cl, halogenated alkyl having up to 6 C atoms,halogenated alkenyl having up to 6 C atoms, halogenated alkenyloxyhaving up to 6 C atoms, or halogenated alkoxy having up to 6 C atoms, Z⁰is —C₂F₄—, —CF═CF—, —C₂H₄—, —(CH₂)₄—, —OCH₂—, —CH₂O—, —CF₂O— or —OCF₂—,Y¹ to Y⁴ are each, independently of one another, H or F, r is 0 or 1,and t is 0, 1 or
 2. 5. A liquid-crystalline medium according claim 1,wherein said medium further comprises one or more compounds selectedfrom formulae XIV and XV:

in which R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having upto 9 C atoms, X⁰ is F, Cl, halogenated alkyl having up to 6 C atoms,halogenated alkenyl having up to 6 C atoms, halogenated alkenyloxyhaving up to 6 C atoms, or halogenated alkoxy having up to 6 C atoms,rings A and B, independently of one another, are each 1,4-phenylenewhich is substituted by 0, 1 or 2 fluorine, and where in each case atleast one of the 1,4-phenylene rings is mono- or polysubstituted byfluorine atoms.
 6. A liquid-crystalline medium according to claim 1,wherein said medium further comprises one or more compounds of formulaeE-a to E-d

in which R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having upto 9 C atoms.
 7. A liquid-crystalline medium according to claim 1,wherein said medium further comprises one or more compounds of formulaeIIa to IIg

in which R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having upto 9 C atoms.
 8. A liquid-crystalline medium according to claim 1,wherein said medium further comprises one or more compounds of formulaeO1 and O2

in which alkyl and alkyl* are each, independently of one another, astraight-chain or branched alkyl group having 1-7 carbon atoms.
 9. Aliquid-crystalline medium according to claim 1, wherein said mediumfurther comprises one or more dioxane compounds of formulae D1 and/or D2

in which R⁰ is n-alkyl, oxaalkyl, fluoroalkyl or alkenyl, each having upto 9 C atoms.
 10. In a method of generating an electro-optical effectusing a liquid-crystalline medium, the improvement wherein said mediumis a liquid-crystalline medium according to claim
 1. 11. Anelectro-optical liquid-crystal display containing a liquid-crystallinemedium according to claim
 1. 12. A compound according to formula Ic

in which R¹ is a halogenated or unsubstituted alkyl or alkoxy radicalhaving 1 to 15 C atoms, where, in addition, one or more CH₂ groups inthese radicals are each, independently of one another, optionallyreplaced by —C≡C—, —CH═CH—, —O—, —CO—O— or —O—CO— in such a way that Oatoms are not linked directly to one another, X is F, Cl, CN, SF₅ or ahalogenated or unsubstituted alkyl or alkoxy radical having 1 to 15 Catoms, where, in addition, one or more CH₂ groups in these radicals areeach, independently of one another, optionally replaced by —C≡C—,—CH═CH—, —O—, —CO—O— or —O—CO— in such a way that O atoms are not linkeddirectly to one another, and L¹, L², L³, L⁴, L⁵ and L⁶ are each,independently of one another, H or F.
 13. A liquid-crystalline mediumaccording to claim 1, wherein 2, 3 or 4 of the substituents L¹, L², L³and L⁴ in the formula I are each hydrogen and the others are each F. 14.A liquid-crystalline medium according to claim 1, wherein L⁵ and L⁶ areeach H.
 15. A liquid-crystalline medium according to claim 1, wherein mis 0, and L¹ or L² are each F; or m is 1 or 2, and L¹ and L² are each H.16. A liquid-crystalline medium according to claim 1, wherein X is F,Cl, OCF₃, CF₃, SF₅, OCHF₂, OC₂F₅, OC₃F₇, OCHFCF₃, OCF₂CHFCF₃ or alkylhaving 1 to 8 C atoms.
 17. A liquid-crystalline medium according toclaim 1, wherein R¹ is an unsubstituted, straight-chain alkyl having 1to 6 C atoms, straight-chain alkoxy having 1 to 6 C atoms, orstraight-chain 2-6 C alkenyl.
 18. A liquid-crystalline medium accordingto claim 1, wherein Z¹ is a single bond or —CF═CF—, Z² is —CF═CF— or—CF₂O—, and m is 0 or
 1. 19. A liquid-crystalline medium according toclaim 1, wherein m is 1 or 2, Z¹ is —CF═CF—, and ring A is a ring systemselected from the formulae

where the rings may point to both sides.
 20. A liquid-crystalline mediumaccording to claim 1, wherein m is 1 or 2, Z is —CF═CF—, and ring A is aring system selected from the formulae

and


21. A liquid-crystalline medium according to claim 1, wherein m is 1, Z²is —CF═CF— and Z¹ is a single bond, X is F, —OCF₃, —CF₃, CN, 1-6 Cn-alkyl or 1-6 C n-alkoxy, L⁵, L⁶ are each H, or R¹ is 1-7 C alkyl or2-7 C alkylene.
 22. A liquid-crystalline medium according to claim 1,wherein Z² is —CF═CF—, and L³ and L⁴ are each H.
 23. Aliquid-crystalline medium according to claim 1, wherein said medium hasa rotational viscosity γ₁ at 20° C. of <80 mPa·s.
 24. Aliquid-crystalline medium according to claim 1, wherein said medium hasa flow viscosity ν₂₀ at 20° C. of <50 mm²·s⁻¹.
 25. A liquid-crystallinemedium according to claim 1, wherein the proportion of compounds of theformula I in the mixture as a whole is from 0.5 to 40% by weight, andthe proportion of compounds of formulae K-1 to K-12 from 5 to 50% byweight.
 26. A liquid-crystalline medium according to claim 4, whereinthe proportion of compounds of formulae II to VI in the mixture as awhole is from 30 to 80% by weight.
 27. A liquid-crystalline mediumaccording to claim 26, wherein the proportion of compounds of theformula I in the mixture as a whole is from 0.5 to 40% by weight, andthe proportion of compounds of formulae K-1 to K-12 from 5 to 50% byweight.
 28. A liquid-crystalline medium according to claim 6, whereinthe proportion of the compounds of formulae E-a to E-d in the mixture asa whole is 5-30% by weight.